Washing and wearing the shirt several times before you come up with final changes is a good idea.
I don't like to discuss values as they have a lot do with your height, weight etc. and I can only guess those from your pictures.
I think your shirt is on the short side even for untucked shirts, so adding some length sounds like a good idea.
The shirt seems to have a pronounced hourglass shape, that I have fallen out of love with.
I have learned that untucked shirts with as...